Cross-linkable polymer blends containing alkoxysilane-terminated polymers

ABSTRACT

Alkoxysilane-terminated polymers prepared by reacting an isocyanatoalkoxysilane, preferably an isocyanatodialkyalkoxysilane, with an isocyanate-reactive prepolymer, can provide chain extension even when a monoalkoxy-functional silane, while retaining suitable reactivity profiles. The products are useful in sealants, caulks, coatings, and moldings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to one-component blends comprisingalkoxysilane-terminated polymers which cure at room temperature underthe action of atmospheric moisture to form low-modulus compositions.

2. Description of the Related Art

Polymer systems which possess reactive alkoxysilyl groups have beenknown for a long time. In the presence of atmospheric moisture thesealkoxysilane-terminated polymers are capable even at room temperature ofundergoing condensation with one another, with the elimination of thealkoxy groups. Depending on the amount and structure of the alkoxysilanegroups, the condensation products are principally long-chain polymers(thermoplastics), relatively wide-meshed three-dimensional networks(elastomers) or else highly crosslinked systems (thermosets).

The polymers concerned may be either alkoxysilane-terminated polymerswith an organic backbone, such as polyurethanes, polyesters, polyethers,etc. described inter alia in EP-A-269 819, EP-A-931 800, WO 00/37533,U.S. Pat. No. 3,971,751 and DE-A-198 49 817, or polymers whose backboneis composed wholly or at least partly of organosiloxanes, describedinter alia in WO 96/34030 and U.S. Pat. No. 5,254,657.

In accordance with the countless possibilities for designing suchsilane-terminated polymer systems, the properties of the uncrosslinkedpolymers or of the polymer-containing mixtures and also the propertiesof the crosslinked compositions (hardness, elasticity, etc.) can beadjusted. Correspondingly diverse, therefore, are the possible uses ofsuch silane-terminated polymer systems. For example, they may be usedfor preparing elastomers, sealants, adhesives, elastic adhesion systems,rigid or flexible foams, and a very wide variety of coating systems, andin the medical sphere, for example for impression compounds in thedental sector. These products can be applied in any form, such as bybrushing, spraying, pouring, pressing, trowelling, etc.

In many systems a substantial disadvantage lies in the contradictoryeffect of chain length or molecular weight of the polymer used and theprocessing properties in terms of the viscosity. High molecular weightsare not only of interest owing to the higher mechanical strengthassociated with them but are also an important prerequisite for thepreparation of low-modulus elastomers, as are required in particular insealants. Where polymers of lower viscosity can be used in suchcompositions, the adjustment of the processing properties becomes muchsimpler and more flexible.

For example, a silicone polymer must be used with a viscosity which isas high as possible in order for the cured product to achieve the rightproperties in terms of ultimate tensile strength and elasticity for usein construction sealants. State of the art here is a polymer having aviscosity of at least 80 Pas. Such a polymer, however, gives rise toadverse properties in the paste, such as stringing, poor smoothability,and high plasticizer content. For setting these properties the idealwould be a polymer having a viscosity of not more than 20 Pas.

This tendency is even more pronounced in the context of the use ofsilane-terminated polyurethanes. Here, it is well-nigh impossible toprepare low-modulus compositions without significantly impairing themechanical properties, generally as a result of additions ofplasticizer.

A great advantage, therefore, would be alkoxysilane-terminated polymersystems which on curing bring about not only crosslinking but also achain extension of the polymers. In order to reduce the crosslinkingdensities it is common to incorporate difunctional silanes into thepolymers. Since the reactivity of such compositions is generally muchlower, it is necessary to raise the amount of catalysts (usuallycontaining tin) sharply. In this context it would be particularlyadvantageous to be able to use not only difunctional silanes but alsomonofunctional silanes, which are able to bring about chain extensionexclusively. The known monofunctional silane end groups, based onsilanes having trimethylene spacers between the organic functional unitand the silicon atom, however, are so slow to react that they generallyfunction as “dead” chain ends.

DE-A 2543966 and DE-A 2445220 describe the use of polymers containingmonofunctional alkoxysilane endgroups for preparing one- andtwo-component polysiloxane-polyurethane copolymers. Here,isocyanate-terminated polyurethanes are reacted withaminomethylmonoalkoxysilanes (especiallycyclohexylaminomethyldimethylethoxysilane) and the polymers obtained arecrosslinked with crosslinker units and OH-terminated polysiloxanes toform elastomers.

One of the disadvantages of this system is the fact that the reaction istied to the use of isocyanate-terminated prepolymers. Polymers of thiskind are normally prepared by reacting excess diisocyanates withpolyols. As a result of the incorporation of the urethane groups, but inparticular as a result of the large number of side reactions occurringwhen an excess of isocyanate is used (biuret formation, formation ofurea bonds through hydrolysis of the NCO groups and condensation withfurther NCO groups, etc.), this generally leads to very viscouspolymers. The incorporation of the aminosilanes to form urea groupsreinforces this negative effect. To compensate for it these polymersmust usually be synthesized with relatively low molecular weights. That,however, adversely affects the elastic behavior of the cured products.In the case of silanes with a functionality of two or three, only verybrittle compositions of high modulus are generally obtained. Theincorporation of monoalkoxy endgroups is certainly advantageous here.However, the modulus of these compositions is always very high and sopresents problems for applications in the construction sealant sector.

As depicted in EP-A-931800, the incorporation of isocyanatosilanesresults in a marked improvement in the properties of the sealants ascompared with corresponding polymers prepared by way of aminosilanes.However, it has not proven possible to date to use monofunctionalsilanes here, since the silanes customary at present, with trimethylenespacers, as already mentioned above, have a reactivity which is much toolow.

SUMMARY OF THE INVENTION

It has now been surprisingly discovered that alkoxysilane-terminatedpolymers prepared by reacting an isocyanatoalkoxysilane, preferably anisocyanatodialkylalkoxysilane, with an isocyanate-reactive prepolymer,can provide chain extension even when they comprisemonoalkoxy-functional silanes, while retaining suitable reactivityprofiles. The cured products exhibit higher tensile strength andelongation, and are both more flexible and softer, than comparableproducts prepared from trialkoxysilane-terminated polymers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The invention provides crosslinkable polymer blends which comprisealkoxysilane-terminated polymers (A) having endgroups of the generalformula (1)-L-CH₂—SiR¹ _(a)(OR²)_(3-a)  (1)the polymers (A) being obtainable by reacting prepolymers (A1)containing reactive HO, HN(R³) or HS endgroups, with isocyanatosilanesof the general formula (2)OCN—CH₂—SiR¹ _(a)(OR²)_(3-a)  (2)where

-   L is a divalent linking group selected from —O—CO—NH—,    —N(R³)—CO—NH—, —S—CO—NH—,-   R¹ is an optionally halogen-substituted alkyl, cycloalkyl, alkenyl    or aryl radical having 1–10 carbon atoms,-   R² is an alkyl radical having 1–6 carbon atoms or an ω-oxyalkylalkyl    radical having a total of 2–10 carbon atoms,-   R³ is hydrogen, an optionally halogen-substituted cyclic, linear or    branched C₁ to C₁₈ alkyl or alkenyl radical or a C₆ to C₁₈ aryl    radical, and-   a is an integer from 0 to 2,    with the proviso that the fraction of the endgroups of the general    formula (1) where a=2, relative to all the endgroups of the polymers    present in the mixture, is from 5% to 100%.

The polymers (A) which possess alkoxysilyl endgroups of the generalformula (1) possess a very high reactivity with respect to moisture.Thus it is also possible to incorporate monoalkoxy endgroups and toprepare and process polymer blends which cure at a sufficiently highrate and with sufficiently short tack-free times at room temperatureeven with small amounts of added heavy metal catalysts or indeed none atall.

It has been found that the hitherto-unexaminedisocyanatomethylalkoxysilanes of the general formula (2) can be usedtogether with prepolymers (A1) that possess reactive HO, NH(R³) or SHendgroups, which can be reacted with the isocyanate group, to preparealkoxysilane-terminated polymers (A) which possess very high curingrates.

Also surprising was the fact that even theisocyanatomethylmonoalkoxysilanes (a=2) are reactive enough to allowmoisture-curing compositions with skinning times of less than 15 minutesto be obtained with them.

A further advantage of the use of isocyanatomethylalkoxysilanes of thegeneral formula (2) is that the one-component polymer blends can also beprepared using relatively low molecular mass prepolymers (A1), which asa result are also much more favorably priced, as polymer buildingblocks; in contrast to the abovementioned aminosilanes it is possible toobtain not only isocyanato-functional systems (NCO-terminatedpolyurethanes) but also a multiplicity of further polymer systems.

The polymer blends comprising polymers (A) crosslink to form low-moduluselastomers which have relatively high chain lengths and molecularweights and as a result attain higher mechanical strength properties andhigher elasticities.

Preferred radicals R¹ are methyl, ethyl or phenyl groups, methyl groupsbeing particularly preferred. The radicals R² are preferably methyl orethyl groups, while preferred radicals R³ are hydrogen, alkyl radicalshaving 1–4 carbon atoms, cyclohexyl and phenyl radicals.

The main chains of the alkoxysilane-terminated polymers (A) may bebranched or unbranched. Depending on the particular properties desired,both of the uncrosslinked mixture and of the cured composition, theaverage chain lengths may be adapted arbitrarily. The polymers may becomposed of various units. These units are normally polysiloxanes,polysiloxane-urea/urethane copolymers, polyurethanes, polyureas,polyethers, polyesters, polyacrylates and polymethacrylates,polycarbonates, polystyrenes, polyamides, polyvinyl esters orpolyolefins such as polyethylene, polybutadiene, ethylene-olefincopolymers or styrene-butadiene copolymers. It is of course alsopossible to use any desired mixtures or combinations of polymers withdifferent main chains.

Where the prepolymer (A1) is itself composed of two or more buildingblocks (A11, A12, etc.), it is not absolutely necessary to use thesebuilding blocks (A11, A12, etc.) first to prepare the prepolymer (A1),which is subsequently reacted with the silane of the general formula (2)to give the finished polymer (A). Thus it is also possible here toreverse the reaction steps, by first reacting one or more buildingblocks (A11, A12, etc.) with a silane of the general formula (2) andonly then reacting the resultant compounds with the remaining buildingblocks (A11, A12, etc.) to give the finished polymer (A).

Examples of such prepolymers (A1) composed of building blocks A11, A12are HO— and HN(R³)-terminated polyurethanes and polyureas, which can beprepared from polyisocyanates (building block A11) and polyols (buildingblock A12).

Preferred building blocks (A11, A12, etc.) for preparing the polymers(A), besides the silanes of the general formula (2), are OH-terminatedpolyols, monomeric alcohols/amines having at least two OH/NH functionsand/or hydroxyalkyl- or aminoalkyl-terminated polydiorganosiloxanes andalso diisocyanates or polyisocyanates.

Particularly suitable polyols for preparing the polymers (A) arearomatic and aliphatic polyesterpolyols and polyetherpolyols, such asare widely described in the literature. In principle, however, it ispossible to use all polymeric, oligomeric or else monomeric alcoholshaving two or more OH functions.

As hydroxyalkyl- or aminoalkyl-terminated polysiloxanes it is preferredto use compounds of the general formula (3)Z-R⁶—[Si(R⁵)₂—O—]_(n)—Si(R⁵)₂—R⁶-Z  (3)in which

-   R⁵ is a hydrocarbon radical having from 1 to 12 carbon atoms,    preferably methyl radicals,-   R⁶ is a branched or unbranched hydrocarbon chain having 1–12 carbon    atoms, preferably trimethylene, and-   n is a number from 1 to 3000, preferably a number from 10 to 1000,    and-   Z means HO or HN(R³), where R³ can be as defined above.

Examples of customary diisocyanates are diisocyanatodiphenylmethane(MDI), both in the form of monomeric or technical-grade MDI and in theform of pure 4,4′- and/or 2,4′-isomers or mixtures thereof, tolylenediisocyanate in the form of its various regioisomers,diisocyanatonaphthalene, isophorone diisocyanate, or else hexamethylenediisocyanate. Examples of polyisocyanates are polymericmethylenediphenyl 4,4′-diisocyanate, triphenylmethane triisocyanate orbiuret triisocyanates.

The fraction of the endgroups of the general formula (1) where a=2,relative to all endgroups in the polymers present in the polymermixture, is preferably at least 25%, more preferably at least 50% and inparticular at least 75%.

Besides the polymers (A) whose endgroups correspond to the generalformula (1) it is also possible for the mixture to include otherpolymers (X) which contain other endgroups. Examples of other polymers(X) are, in the case of the polydiorganosiloxanes, preferablytrimethylsilyl-terminated polymethylsiloxanes or certain aromatics-freehydrocarbons. In the case of the pure organic polymer systems they arephthalates, adipates, alkylsulfonates or, again, aromatics-freehydrocarbons. These polymers preferably serve as plasticizers and forsetting the rheology of the compositions.

Preferably at least 60% by weight, with particular preference at least80% by weight, in particular at least 90% by weight of polymers (A) arepresent in a mixture, based on the sum of the polymers (A) and (X).

The polymer mixtures may further comprise catalysts as component (B).Catalysts in this context are compounds capable of catalyzing the curingof the polymer blend. In particular the catalysts in question areorganic heavy metal compounds. Heavy metals in this context are allmetals apart from the light metals, i.e. apart from the alkali metalsand alkaline earth metals and also aluminum and scandium. The polymerblends are preferably free from catalysts containing tin, especiallyorganotin compounds, with the absence of catalysts containing titaniumlikewise being preferred. With particular preference the polymer blendsare free from any catalysts containing heavy metals.

In the polymer blends it is preferably also possible to use, ascomponent (B), organic amino compounds as basic catalysts. Examples areaminosilanes, such as aminopropyltrimethoxysilane,aminopropyltriethoxysilane, aminomethyltrimethoxysilane,aminomethylmethyltrimethoxysilane,N-(2-aminoethyl)aminopropyltrimethoxysilane and aliphatic hydrocarbonamines such as triethylamine, tributylamine,1,4-diazabicyclo[2.2.2]octane,N,N-bis-(N,N-dimethyl-2-aminoethyl)methylamine,N,N-dimethylcyclohexylamine, N,N-dimethylphenylamine andN-ethylmorpholine.

The catalysts are preferably used in concentrations of 0.01–10% byweight, in particular from 0.05 to 3% by weight, in the polymer blend.The various catalysts may be used either in pure form or as mixtures ofdifferent catalysts.

As a further component (C) the polymer blends may include what are knownas crosslinker silanes. These are organofunctional silanes orcondensates thereof having at least three alkoxy groups, especiallymethoxy and ethoxy groups, per molecule. Examples of such trifunctionalsilanes are methyltrimethoxysilane, ethyltrimethoxysilane,phenyltrimethoxysilane, vinyltrimethoxysilane and partial hydrolysatesthereof. The crosslinker silanes may be present in amounts of 0.01–20%by weight, preferably 1.0–5.0% by weight, in the finished polymer blend.

As further components the polymer blends may include auxiliaries knownper se, such as fillers, water scavengers, reactive diluents, adhesionpromoters, thixotropic agents, light stabilizers, fungicides, flameretardants, pigments, etc., such as are known for use in conventionalalkoxy-crosslinking one-component compositions. Such additions aregenerally vital in order to produce the particular profiles ofproperties that are desired both in the uncrosslinked polymer blends andin the cured compositions.

A very wide variety of applications exists for the polymer blends in thefields of adhesives, sealants, including joint sealants, and surfacecoatings and also for producing moldings.

The blends are suitable for a wide variety of substrates, such asmineral substrates, metals, plastics, glass and ceramic, for example.

The polymer blends can be employed both in pure form and in the form ofsolutions or dispersions.

All of the above symbols in the above formulae have their definitions ineach case independently of one another. In all formulae the silicon atomis tetravalent.

In the examples below, unless indicated otherwise, all amounts andpercentages are by weight, all pressures are 0.10 MPa (abs.) and alltemperatures are 20° C.

The skinning times were determined by testing the surface with a metalspatula. The skinning time is the time at which, when the surface iscontacted, either the spatula no longer adheres or, if it does adhereslightly, stringing has ceased.

EXAMPLE 1

Preparation of isocyanatomethyltrimethoxysilane:Methylcarbamatomethyltrimethoxysilane is pumped in a stream of argon gasinto a quartz pyrolysis tube packed with quartz wool. The temperature inthe pyrolysis tube is between 420 and 470° C. At the end of the heatedsection, the crude product is condensed out by means of a condenser andcollected. The yellowish brown liquid is purified by distillation underreduced pressure. The desired product passes over at the top at about88–90° C. (82 mbar) in a purity of more than 99%, while at the bottomthe unreacted carbamate can be reisolated. It is passed back directly tothe pyrolysis.

EXAMPLE 2

a) Preparation of isocyanatomethyldimethylmethoxysilane:Methylcarbamatomethyldimethylmethoxysilane is reacted to form theisocyanate by pyrolysis in analogy to Example 1. The yellowish brownliquid is purified by distillation under reduced pressure. The desiredproduct passes over at the top at about 59–60° C. (20 mbar) in a purityof more than 99%.

b) Preparation of isocyanatomethyldimethylethoxysilane:Methylcarbamatomethyldimethylethoxysilane is reacted to form theisocyanate by pyrolysis in analogy to Example 1 and 2a). The yellowishbrown liquid is purified by distillation under reduced pressure. Thedesired product passes over at the top at about 66–69° C. (20 mbar) in apurity of more than 99%.

Comparative Example C3 (Not According to the Invention)

500 g (11.1 mmol) of α,ω-(3-aminopropyl)polydimethylsiloxane having anaverage molecular weight of 45 000 g/mol are heated to 80° C. in aheatable laboratory planetary mixer equipped with vacuum pump and areheated to completion in vacuo for 0.5 h. Then 3.9 g (22.2 mmol) ofisocyanatomethyltrimethoxysilane are added at 80° C. and stirring iscontinued for an hour. Complete conversion of the silane is monitoredusing IR spectroscopy, on the basis of the NCO band.

The silane-terminated polymer obtained is cooled to 25° C. withstirring, 230.0 g of a trimethylsilyl-terminated polydimethylsiloxanehaving a viscosity of 100 Pas, 20.0 g of methyltrimethoxysilanes and85.0 g of a hydrophilic pyrogenic silica are added and the mixture isprocessed within 0.5 h to form a stiff paste. Finally, 8.0 g of3-(2-aminoethyl)aminopropyltrimethoxysilane, as a further crosslinkerand catalyst, are mixed in for 10 minutes.

The paste is applied by knifecoating in a layer thickness of 2 mm to aTeflon plate and is crosslinked to form a silicone rubber under theaction of atmospheric moisture. After the mixture has been applied, thetack-free time in air is approximately 5 minutes (23° C., 50% rh). Thecharacteristics of this product are summarized in Table 1.

Comparative Example C4 (Not According to the Invention)

500 g (11.1 mmol) of α,ω-(3-aminopropyl)polydimethylsiloxane having anaverage molecular weight of 45 000 g/mol are heated to 80° C. in aheatable laboratory planetary mixer equipped with vacuum pump and areheated to completion in vacuo for 0.5 h. Then 4.6 g (22.2 mmol) ofisocyanatopropyltrimethoxysilane (Silquest Y-5187 from Crompton) areadded at 80° C. and stirring is continued for an hour. Completeconversion of the silane is monitored using IR spectroscopy, on thebasis of the NCO band.

The silane-terminated polymer obtained is cooled to 25° C. withstirring, 230.0 g of a trimethylsilyl-terminated polydimethylsiloxanehaving a viscosity of 100 Pas, 20.0 g of methyltrimethoxysilanes and85.0 g of a hydrophilic pyrogenic silica are added and the mixture isprocessed within 0.5 h to form a stiff paste. Finally, 8.0 g of3-(2-aminoethyl)aminopropyltrimethoxysilane, as a further crosslinker,are mixed in for 10 minutes.

The paste is applied by knifecoating in a layer thickness of 2 mm to aTeflon plate and is crosslinked to form a silicone rubber under theaction of atmospheric moisture. After the mixture has been applied, thetack-free time in air is approximately 2 hours (23° C., 50% rh). Thecharacteristics of this product are summarized in Table 1.

EXAMPLE 5 (According to the Invention)

500 g (11.1 mmol) of α,ω-(3-aminopropyl)polydimethylsiloxane having anaverage molecular weight of 45 000 g/mol are heated to 80° C. in aheatable laboratory planetary mixer equipped with vacuum pump and areheated to completion in vacuo for 0.5 h. Then 3.6 g (22.2 mmol) ofisocyanatomethyldimethylmethoxysilane are added at 80° C. and stirringis continued for an hour. Complete conversion of the silane is monitoredusing IR spectroscopy, on the basis of the NCO band.

The silane-terminated polymer obtained is cooled to 25° C. withstirring, 230.0 g of a trimethylsilyl-terminated polydimethylsiloxanehaving a viscosity of 100 Pas, 20.0 g of methyltrimethoxysilane and 85.0g of a hydrophilic pyrogenic silica are added and the mixture isprocessed within 0.5 h to form a stiff paste. Finally, 20.0 g of3-(2-aminoethyl) aminopropyltrimethoxysilane, as a further crosslinkerand catalyst, are mixed in for 10 minutes.

The paste is applied by knifecoating in a layer thickness of 2 mm to aTeflon plate and is crosslinked to form a silicone rubber under theaction of atmospheric moisture. After the mixture has been applied, thetack-free time in air is approximately 25 minutes (23° C., 50% rh). Thecharacteristics of this product are summarized in Table 1.

Comparative Example C6 (Not According to the Invention)

400 g (50.0 mmol) of a polypropylene glycol having an average molecularweight of 8000 g/mol are introduced, dewatered in vacuo at 100° C. for 1h and polymerized with 12.5 g (56 mmol) of isophorone diisocyanate at100° C. over the course of 60 minutes. The OH-terminated polyurethaneprepolymer obtained is subsequently cooled to 60° C., 19.5 g (110 mmol)of isocyanatomethyltrimethoxysilane are added and the mixture is stirredfor 60 minutes until the isocyanate band is no longer present in the IRspectrum. The product is a clear, transparent polymer having a viscosityof 85 Pas.

In a laboratory planetary mixer, the silane-terminated polymer thusprepared is admixed at about 25° C. with 95 g of diisoundecyl phthalate,20.0 g of methyltrimethoxysilane and 430 g of precipitated, dried chalk(dried beforehand, water content <50 ppm) and processed to form a stiffpaste. Finally, 20.0 g of 3-(2-aminoethyl)aminopropyltrimethoxysilane,as a further crosslinker and catalyst, are mixed in for 10 minutes.After the mixture has been applied the tack-free time in air isapproximately 5 minutes (23° C., 50% rh). The characteristics of thisproduct are summarized in Table 1.

EXAMPLE 7 (According to the Invention)

400 g (50.0 mmol) of a polypropylene glycol having an average molecularweight of 8000 g/mol are introduced, dewatered in vacuo at 100° C. for 1h and polymerized with 12.5 g (56 mmol) of isophorone diisocyanate at100° C. over the course of 60 minutes. The OH-terminated polyurethaneprepolymer obtained is subsequently cooled to 60° C., 17.7 g (110 mmol)of isocyanatomethyldimethylmethoxysilane are added and the mixture isstirred for 60 minutes until the isocyanate band is no longer present inthe IR spectrum. The product is a clear, transparent polymer having aviscosity of 80 Pas.

In a laboratory planetary mixer, the silane-terminated polymer thusprepared is admixed at about 25° C. with 95 g of diisoundecyl phthalate,20.0 g of methyltrimethoxysilane and 430 g of precipitated, dried chalk(dried beforehand, water content <50 ppm) and processed to form a stiffpaste. Finally, 20.0 g of 3-(2-aminoethyl)aminopropyltrimethoxysilane,as a further crosslinker and catalyst, are mixed in for 10 minutes.

After the mixture has been applied the tack-free time in air isapproximately 20 minutes (23° C., 50% rh). The characteristics of thisproduct are summarized in Table 1.

Comparative Example C8 (Not According to the Invention)

400 g (50.0 mmol) of a polypropylene glycol having an average molecularweight of 8000 g/mol are introduced, dewatered in vacuo at 100° C. for 1h and admixed with 19.5 g (110 mmol) ofisocyanatomethyltrimethoxysilane, and the mixture is stirred for 60minutes until the isocyanate band is no longer present in the IRspectrum. The product is a clear, transparent polymer having a viscosityof 8.5 Pas.

In a laboratory planetary mixer, the silane-terminated polymer thusprepared is admixed at about 25° C. with 13.0 g ofmethyltrimethoxysilane and 195 g of precipitated, dried chalk (driedbeforehand, water content <50 ppm) and processed to form a stiff paste.

Finally, 13.0 g of 3-(2-aminoethyl)aminopropyltrimethoxysilane, as afurther crosslinker and catalyst, are mixed in for 10 minutes. After themixture has been applied the tack-free time in air is approximately 3minutes (23° C., 50% rh). The characteristics of this product aresummarized in Table 1.

EXAMPLE 9 (According to the Invention)

400 g (50.0 mmol) of a polypropylene glycol having an average molecularweight of 8000 g/mol are introduced, dewatered in vacuo at 100° C. for 1h and admixed with 15.9 g (110 mmol) ofisocyanatomethyldimethylmethoxysilane, and the mixture is stirred for 60minutes until the isocyanate band is no longer present in the IRspectrum. The product is a clear, transparent polymer having a viscosityof 85 Pas.

In a laboratory planetary mixer, the silane-terminated polymer thusprepared is admixed at about 25° C. with 13.0 g ofmethyltrimethoxysilane and 195 g of precipitated, dried chalk (driedbeforehand, water content <50 ppm) and processed to form a stiff paste.Finally, 13.0 g of 3-(2-aminoethyl)aminopropyltrimethoxysilane, as afurther crosslinker and catalyst, are mixed in for 10 minutes. After themixture has been applied the tack-free time in air is approximately 15minutes (23° C., 50% rh). The characteristics of this product aresummarized in Table 1.

EXAMPLE 10 (According to the Invention)

400 g (50.0 mmol) of a polypropylene glycol having an average molecularweight of 8000 g/mol are introduced, dewatered in vacuo at 100° C. for 1h and admixed with 17.3 g (110 mmol) ofisocyanatomethyldimethylethoxysilane, and the mixture is stirred for 60minutes until the isocyanate band is no longer present in the IRspectrum. The product is a clear, transparent polymer having a viscosityof 80 Pas.

In a laboratory planetary mixer, the silane-terminated polymer thusprepared is admixed at about 25° C. with 195 g of precipitated, driedchalk (dried beforehand, water content <50 ppm) and processed to form astiff paste. Finally, 26.0 g of3-(2-aminoethyl)aminopropyltriethoxysilane, as a further crosslinker andcatalyst, are mixed in for 10 minutes. After the mixture has beenapplied the tack-free time in air is approximately 10 minutes (23° C.,50% rh). The characteristics of this product are summarized in Table 1.

TABLE 1 Properties of the one-component mixtures Comp. Comp. Comp. Comp.Characteristic Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Skinning5 120 25 5 20 3 15 10 [min] Tensile 1.49 1.35 1.82 1.45 2.05 1.60 2.172.34 strength [MPa], DIN 53504 Elongation 396 422 635 220 475 120 465498 at break [%], DIN 53504 Stress at 100% 0.48 0.45 0.35 0.75 0.67 1.300.85 0.80 elongation [MPa], DIN 53504 Hardness 18 16 16 55 46 56 25 25[Shore A], DIN 53505

1. A crosslinkable polymer blend, comprising at least one polymer Ahaving endgroups of the formula (1)-L-CH₂—SiR¹ _(a)(OR²)_(3-a)  (1) wherein L is a divalent linking groupselected from —O—CO—NH—, —N(R³)—CO—NH—, —S—CO—NH—, R¹ is an optionallyhalogen-substituted alkyl, cycloalkyl, alkenyl or aryl radical having1–10 carbon atoms, R² is an alkyl radical having 1–6 carbon atoms or anω-oxyalkylalkyl radical having a total of 2–10 carbon atoms, R³ ishydrogen, an optionally halogen-substituted cyclic, linear or branchedC₁ to C₁₈ alkyl or alkenyl radical or a C₆ to C₁₈ aryl radical, and a isan integer from 0 to 2, with the proviso that the fraction of theendgroups of the general formula (1) where a=2, relative to all theendgroups of the polymers present in the mixture which have alkoxysilaneendgroups, is from 5% to 100%.
 2. The polymer blend of claim 1, whereinthe fraction of the endgroups of the general formula (1) where a=2,relative to all the endgroups of the polymers present in the polymermixture which have alkoxysilane endgroups, is at least 50%.
 3. Thepolymer blend of claim 1, wherein the radicals R¹ are independentlymethyl, ethyl or phenyl radicals.
 4. The polymer blend of claim 2,wherein the radicals R¹ are independently methyl, ethyl or phenylradicals.
 5. The polymer blend of claim 1, wherein the radicals R² areindependently methyl or ethyl radicals.
 6. The polymer blend of claim 2,wherein the radicals R² are independently methyl or ethyl radicals. 7.The polymer blend of claim 3, wherein the radicals R² are independentlymethyl or ethyl radicals.
 8. The polymer blend of claim 1, furthercomprising at least one organic amino compound as a basic catalyst (B).9. The polymer blend of claim 3, further comprising at least one organicamino compound as a basic catalyst (B).
 10. The polymer blend of claim5, further comprising at least one organic amino compound as a basiccatalyst (B).
 11. In an adhesive, sealant, coating, or moldableelastomer which is moisture curable and which contains a blend of one ormore alkoxysilane-functional polymers, the improvement comprisingselecting as said blend, a crosslinkable polymer blend of claim
 1. 12.In an adhesive, sealant, coating, or moldable elastomer which ismoisture curable and which contains a blend of one or morealkoxysilane-functional polymers, the improvement comprising selectingas said blend, a crosslinkable polymer blend of claim
 2. 13. In anadhesive, sealant, coating, or moldable elastomer which is moisturecurable and which contains a blend of one or morealkoxysilane-functional polymers, the improvement comprising selectingas said blend, a crosslinkable polymer blend of claim
 3. 14. In anadhesive, sealant, coating, or moldable elastomer which is moisturecurable and which contains a blend of one or morealkoxysilane-functional polymers, the improvement comprising selectingas said blend, a crosslinkable polymer blend of claim
 5. 15. In anadhesive, sealant, coating, or moldable elastomer which is moisturecurable and which contains a blend of one or morealkoxysilane-functional polymers, the improvement comprising selectingas said blend, a crosslinkable polymer blend of claim
 8. 16. A processfor the preparation of an alkoxysilane-functional polymer suitable foruse in the crosslinkable polymer blend of claim 1, said processcomprising reacting at least one isocyanatosilane of the formula (2)OCN—CH₂—SiR¹ _(a)(OR²)_(3-a)  (2) with one or more prepolymers having atleast one terminal isocyanate-reactive end group selected from the groupconsisting of OH, HNR^(3,) and HS, wherein R¹ is an alkyl radical having1 to 6 carbon atoms or an ω-oxyalkyl radical having a total of 2 to 10carbon atoms; and a is an integer from 0 to 2, with the proviso that thefraction of the isocyanatosilanes of the formula (2) where a=2 relativeto all isocyanatosilanes which bear SiR¹ _(a) (OR²)_(3-a) groups is from5% to 100%.
 17. The process of claim 16 wherein said prepolymer is alinear polymer selected from the group consisting of polysiloxanes,polysiloxane-urea/urethane copolymers, polyurethanes, polyureas,polyethers, polyesters, poly(meth)acrylates, polycarbonates,polystyrenes, polyamindes, polyvinyl esters, styrene/butadienecopolymers, and polyolefins.
 18. The process of claim 17 wherein saidprepolymer is α, ω-bis-terminated with a single type of isocyanatereactive end group.
 19. A crosslinkable blend comprising at least onealkoxysilane-functional polymer prepared by the process of claim 16.